DW injectors are designed to fit the OE manifold and fuel rail. The use of aftermarket fuel rails and manifolds may cause some fitment issues. Make sure all injector parts are intact and undamaged. Make sure to lubricate the O-rings with the included super lube. Make sure no OE parts from fuel rail or manifold are missing (spacers). If you changed to aftermarket fuel rails or intake manifolds, it would be prudent to contact our technical support for insight on determining if our injectors will fit your application.